This invention relates to a novel control circuit for energizing an inductive load, and more particularly relates to a novel power source and energizing circuit for the inductive drive coils of printer hammers.
Circuits for controlling printer hammer drives are well known. These circuits commonly employ transistors which develop a current pulse which is applied to the printer hammer drive or other similar inductive load. Commonly, two transistors and two associated diodes are provided for each drive coil. The transistors are turned on and off in a sequence to produce a rapidly rising current pulse which stays on for a given time and, after a predetermined time, is turned off with a sharply declining current wave shape. During the time the pulse current flows, the transistors are controlled to keep the pulse current between predetermined maximum and minimum values.
Identical pairs of transistors and diodes are provided for each of a large number of drive coils of a given printer. Commonly, sets of 64 drive coils and hammers are provided for a typical printer. Since four discrete components are required for each coil, the circuits are costly, relatively unreliable and inefficient.